Selective Ethane/Ethylene Separation in a Robust Microporous Hydrogen-Bonded Organic Framework

The separation of ethane (C2H6)
from ethylene
(C2H4) is of prime importance in the production
of polymer-grade C2H4 for industrial manufacturing.
It is very challenging and still remains unexploited to fully realize
efficient C2H6/C2H4 separation
in the emerging hydrogen-bonded organic frameworks (HOFs) due to the
weak nature of hydrogen bonds. We herein report the benchmark example
of a novel ultrarobust HOF adsorbent (termed as HOF-76a) with a Brunauer–Emmett–Teller
surface area exceeding 1100 m2 g–1, exhibiting
the preferential binding of C2H6 over C2H4 and thus highly selective separation of C2H6/C2H4. Theoretical calculations
indicate the key role of the nonpolar surface and the suitable triangular
channel-like pores in HOF-76a to sterically “match”
better with the nonplanar C2H6 molecule than
the planar C2H4, thus affording overall stronger
multipoint van der Waals interactions with C2H6. The exceptional separation performance of HOF-76a for C2H6/C2H4 separation was clearly demonstrated
by gas adsorption isotherms, ideal adsorbed solution theory calculations,
and simulated and experimental breakthrough curves. Breakthrough experiments
on HOF-76a reveal that polymer-grade ethylene gas can be straightforwardly
produced from 50/50 (v/v) C2H6/C2H4 mixtures during the first adsorption cycle with a high
productivity of 7.2 L/kg at 298 K and 1.01 bar and 18.8 L/kg at 298
K and 5.0 bar, respectively.

乙烷（C₂H₆）与乙烯（C₂H₄）的分离，对于工业制备聚合级乙烯（C₂H₄）而言至关重要。由于氢键作用本身较为微弱，在新兴的氢键有机框架（hydrogen-bonded organic frameworks, HOFs）材料中实现高效的乙烷/乙烯分离仍极具挑战，目前尚未得到充分开发。本文报道了一款新型超高稳定性氢键有机框架吸附剂（命名为HOF-76a），作为该领域的标杆实例，其布鲁诺尔-埃米特-特勒（Brunauer–Emmett–Teller, BET）比表面积超过1100 m²·g⁻¹，对乙烷展现出相较于乙烯的优先吸附结合特性，因此可实现高选择性的乙烷/乙烯分离。理论计算表明，HOF-76a的非极性表面与规整的三角形通道状孔道，相较于平面结构的乙烯分子，能够与非平面结构的乙烷实现更优的空间匹配，从而与乙烷形成更强的多点范德华相互作用。通过气体吸附等温线、理想吸附溶液理论（ideal adsorbed solution theory, IAST）计算以及模拟与实验穿透曲线，充分验证了HOF-76a用于乙烷/乙烯分离的优异性能。针对HOF-76a的穿透实验结果显示，在首个吸附循环中，可直接从体积比为50/50（v/v）的乙烷/乙烯混合气体中制备得到聚合级乙烯，在298 K、1.01 bar条件下的产率可达7.2 L/kg，在298 K、5.0 bar条件下产率可达18.8 L/kg。